We have an issue where the RadEditor context menu for <td> element doesn't get displayed. It throws a "Permission Denied" error. Within <td> the table toolbar is not functional either. 
To reproduce: In an aspx page, create an updatepanel with a LoadContent button, RadEditor and Save button.
1. Click on Load Contents button
2. RadEditor with text "Loaded" will get displayed
3. Insert a table
4. Go to a table cell and verify context menu for td shows fine
5. Click Save
6. Go to a table cell and right click - context menu doesn't show (If you have IE developers tool, you will see "Permission Denied" error.)

ASPx page:
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" runat="server">
    <asp:UpdatePanel ID="upd" runat="server">
        <ContentTemplate>
              <asp:Button ID="btnLoad" runat="server" Text="Load Contents"  OnClick="btnLoad_Click"  />
              <telerik:RadEditor ID="HTMLEditor" runat="server"></telerik:RadEditor>          
                <asp:Button ID="btnSave" runat="server" Text="Save"  OnClick="btnSave_Click" UseSubmitBehavior="false" />
        </ContentTemplate>
    </asp:UpdatePanel>     
</asp:Content>
C# Code:
 protected void Page_Load(object sender, EventArgs e)
        {
        }
        protected void btnSave_Click(object sender, EventArgs e)
        { 
            HTMLEditor.Content = HTMLEditor.Content + " updated";            
        }
        protected void btnLoad_Click(object sender, EventArgs e)
        {
            HTMLEditor.Content = "Loaded";
        }